Pythagoras's Theorem/Historical Note
Historical Note on Pythagoras's Theorem
Pythagoras's Theorem, or at least certain specific instances of it, was known to the ancient Egyptians, and it may date back further than that.
Little is actually known about Pythagoras himself, and it is uncertain whether he actually proved it or not.
Some traditional sources suggest that when he discovered this theorem, he was so delighted he sacrificed an ox to the gods in thanksgiving. However, given his philosophical outlook, this is vanishingly unlikely.